Thermal treatment of hydrocarbons



Patented Feb. 21, 1939 THERMAL TREATMENT OF mnmo- CARBONS nuns Haeuber and Fritz Winkler, Ludwlgshatcnon-the-Rhine, Germany, assignors to I. G. Farbenindustrie Aktiengesellschaft, Frankfort-onthe-Main, Germany No Drawing. Application October 29, 1936, Se-

rial No. 108,217. 1935 In Germany November 8,

3 Claims. (Cl. 196-10) The present invention relates to improvements in' the thermal treatment of hydrocarbons, in particular in the splitting of hydrocarbons and in polymerisation reactions at elevated tempera,

tures.

In these processes there is the danger that carbon may be deposited in the reaction vessel and in the pipe conduits. Even when using the usual chromium steels as the constructional materials for the apparatus in which the hydrocarbons are subjected to a thermal treatment, the said danger exists even though only to a slight extent.

border to avoid this drawback it has already been proposed to coat the apparatus or parts thereof after shaping with silicon by burning the latter in in the form of powder. No formation of coke takes-place in apparatus prepared in this way.

We have now found that, contrary to expectation, in the thermal treatment of hydrocarbons an advantageous prevention of the deposition of carbon is obtained in a simple manner by constructing the apparatus wholly or partly from a chromium steel which has a silicon content of more than 1 per cent, advantageously of from 1 to 3 per cent. It is also possible to employ chromium steels containing less than 1 per cent of silicon, namely provided the nickel content of the chromium steel which is ordinarily 1-2 per cent is less than 0.2 per cent. Chromium steels, the chromium content of which is more than 25 per cent, are especially suitable.

When working in apparatus of such alloys, the deposition of carbon is completely avoided. The alloys lose this surprising and important property, however, when the silicon content falls below l per cent unless at the same time the nickel content of the alloy falls below 0.2 per cent. The alloys need contain no other metal besides iron, chromium and silicon.

Apparatus of the said steels are suitable for a great variety of thermal reactions of hydrocarbons, as for example the cracking or polymerization of hydrocarbons in the liquid and especially in the gaseous phase, in one or more stages at atmospheric, increased or reduced pressure and in the presence or absence of catalysts, gases or other additions. The chromium steel alloys containing silicon are especially suitable for apparatus'in which high temperatures, as for example from 500 to 800-C., are used because at such high temperatures trouble by reason of deposition of carbon may occur especially readily.

The shape of the reaction vessels may be as desired; pipes having circular or rectangular cross-section have proved suitable. Filler bodies which may if desired be introduced into the reaction vessels in the thermal treatment of hydrocarbons may also consist of the said steel containing silicon.

The following examples will further illustrate the nature of this invention but the invention is not restricted to these examples.

Example 1 800 litres of gaseous propane (propane content about 95 per cent) which have been preheated to about 300 centigrade are led per hour through a tube of chromium steel having the composition: 30 to 31 per cent of chromium, from about 6'7 to 68 per cent of iron, about 1.4 per cent of silicon and the remainder impurities and the like, the tube being about 5 metres long and about 20 millimetres in internal diameter, being built vertically into a cracking apparatus and being directly heated by fire gases according to the circulating gas process so that it has a temperature of about 840 centigrade in the middle, 810 centigrade at the top and 790 centigrade at the bottom.

In this manner about 1.6 cubic metres of a final gas having the following composition are obtained:-

Per cent by volume Higher olefines 10 C2H4 28 Hz Methane homologues 6 CH4 41 Example 2 1000 litres of butane of a degree of purity of about 90 per cent are led per hour through a tube about 5.5 metres long having an internal diameter of about millimetres which is constructed from a chromium steel which, in addition to iron, contains about 31 per cent of chromium, from 0.4 to 0.8 per cent of silicon and I less than 0.2 per cent of nickel. The tube is directly heated by fire gases by the circulating gas method in such manner that the temperature of the heating gas is about 825 centigrade in the middle of the tube, 800 centigrade at the upper end and 740 centigrade at the lower end. The final gas, the volume of which is about twice that of the gas introduced, has the following composition:

Per cent Higher olefines "about... Ethylene about 13 Hydrogen about 10 Methane homologues about 15 Methane about 37' In addition, for each cubic metre of butane introduced, about grams of a low-boiling product are obtained of which '75 per cent boil up to 200 centigrade. No deposition of carbon can be observed even after working for days.

If, on the other hand, the same reaction be carried out in the same manner in apparatus constructed from a commercial chromium steel containing silicon, which contains 28 per cent of chromium, 0.4 per cent of silicon and 0.49 per cent of nickel, an appreciable deposition of carbon can be observed in the reaction tube,

even after six hours.

What we claim is:

1. Process for preventing carbon deposition in the thermal treatment of hydrocarbons wherein carbon is normally deposited, which comprises carrying out said treatment in apparatus constructed, at least insofar as it is in contact with the reacting materials, of a nickel-chromium steel containing more than 25 per cent of chromium, less than 2 per cent of nickel and between 0.4 and about 3 per cent of silicon, the silicon and the nickel being so proportioned that alloys containing more than 0.2 but less than 2 per cent of nickel contain from about 1 per cent to about 3 per cent of silicon, and alloys containing less than 1 per cent and as low as 0.4 per cent of silicon contain less than 0.2 per cent of nickel.

2. The process for preventing carbon deposition in the thermal treatment of hydrocarbons, wherein carbon is normally deposited, which comprises carrying out the treatment in apparatus constructed, at least insofar as it is in contact with the reacting material, of a nickelchromium steel containing more than 25 per cent of chromium, 0.4 to 0.8 per cent of silicon, and an amount of nickel below 0.2 per cent.

3. The process for preventing carbon deposition in the thermal treatment of hydrocarbons, wherein carbon is normally deposited, which comprises carrying out the treatment in apparatus constructed, at least insofar as it is in contact with the reacting material, of a chromium steel containing more than 25 per cent of chromium, about 1 to about 3 per cent of silicon and more than 0.2 but less than 2 per cent of nickel.

HANS HAEUBER. FRITZ WINKLER. 

